Thermography inspection, such as infrared thermography inspection, is a nondestructive inspection method that is commonly utilized in field inspection of structures, such as aircraft structures. Thermography inspection utilizes the transfer of energy into an object of inspection to generate heat and detects heat energy (e.g., infrared light) that is dissipated from the object. In a particular example, thermography (e.g., infrared thermography) is used to inspect wing and stabilizer components that are fabricated from aluminum honeycomb which may be adhesively bonded between two aluminum or composite face sheets of varying thicknesses. A common defect to inspect for in such structures is a disbond, or separation of the aluminum honeycomb core from one of the two face sheets.
Depending on a particular technique (e.g., a one-side technique or a two-sided technique) of the thermography inspection, a disbond or other defect may appear as a “cool” spot or a “hot” spot. For example, when applying heat (e.g., light) to a first surface of a component of an aircraft, such as an airframe, and imaging a second surface of the component, a defect may appear as a “cool” spot. To illustrate, a lack of continuity in the component (e.g., in a frame or structure positioned between surfaces of the component) causes less heat to be transferred from the first surface to the second surface and causes less heat to be emitted from the second surface, which may be indicated as a cool spot in a thermographic image of the component relative to other portions of the component (e.g., defect free portions). As another example, when applying heat (e.g., light) to a surface of the component and imaging the same surface of the component, a disbond or other defect may appear as a “hot” spot. To illustrate, a lack of continuity in the component (e.g., in a frame or structure underlying the surface of the component) causes less heat to be transferred from the surface to a frame or structure that underlies the surface and causes more heat to be retained and emitted from the surface, which may be indicated as a hot spot in the thermographic image relative to other portions of the component.
Because thermography inspection often utilizes flashlamps to inject a heat generating energy pulse into the component, bare metal or very light colored surfaces of the component may reject incident energy and distort thermographic emitted infrared readings. In such situations, a majority of the light (e.g., heat) may be reflected by the component and therefore is not transfer into and absorbed by the component. Reflection of the light from a flashlamp may reduce the usefulness of a thermographic image of the component used to identify a location of a defect of the component. To reduce reflection of the light, a coating may be applied to a bare metal surface (or other surface) of the component to enable a more uniform heat transfer. Before applying the coating, the surface of the component of the aircraft is prepared by cleaning the surface, and after performance of a thermographic inspection, the surface of the component is cleaned (e.g., using a solvent) before the aircraft is ready for use.
Different coatings may be used as part of the thermographic inspection process. However, coatings may be applied non-uniformly, causing variations in heat transfer into the part and infrared emission from the part. Additionally, an overly thick coating may act as an insulator. To illustrate, an overly thick coating may impede heat transfer into the part, may impede infrared emission from the part, or both. As a particular example, the coating may include flat black paint. The flat black paint may be a water-soluble tempera that is applied to a surface of the component by spraying or brushing. A thermographic inspection may begin after the flat black paint has dried, which increases an amount of time associated with preparing for and performing the thermographic inspection. Additionally, the flat black paint coating is prone to scratches that may occur when a thermographic image capture device contacts the coated surface of the component during thermographic inspection process. The scratches may generate visual interference and may reduce detection of small flaws during analysis of a captured thermographic image of the component.
As another particular example, the coating may include a layer of lampblack coating. The lampblack coating is carbon black (e.g., a black pigment made from soot or other fine carbon powder) with a solvent carrier, such as an aerosol product. While application of the lampblack coating is faster than application of the flat black paint, the application of the lampblack coating is messy and often results in overspray. Additionally, an amount of time spent cleaning the component after the thermographic inspection is complete may be longer than an amount of time to remove the flat black paint. Thus, with current thermography techniques (e.g., using the flat black paint or the lampblack coating) surface preparation and cleaning account for a significant portion of the thermographic inspection process.